Aromatic haloamines are an important class of industrial intermediates for the synthesis of organic fine chemicals, such as dyes, drugs, herbicides and pesticides. The main routes of synthesis of the haloamines involved reduction of corresponding nitrocompounds catalysed by either metal-acid systems or with noble metal. Processes involving later route are favored now a days due to environmental issues associated with the use of hydrochloric acid in the former route.
Control of selectivity is the critical problem while carrying out hydrogenation of halonitroaromatics with noble metals. Apart from the formation of alogenated aromatic amines, extensive dehalogention by cleaving the carbon-halogen bond also occurs. In addition, by-products such as azo and azoxyhalobenzenes are also formed. Furthermore, hydrogen chloride which is produced by the dehalogenation reaction greatly contributes to the corrosion of the reactor.
Attempts were done to minimize the side reaction by the addition of selectivity promoters or dehalogenated inhibitor such as bases or other electron donating compounds along with noble metal catalyst. Numerous efforts (Greenfield et. al. J. Organic Chem., 1967, Vol. 32, Page 3670-3671) are being done to suppress the dehalogenation reaction and to minimize other by-products, including a method of using sulfides of noble metal as a catalyst and a method of adding dehalogenation inhibitor. Disadvantages of using noble metal sulphides are low catalytic activity and complicated preparation processes of these catalysts.
In U.S. Pat. No. 4,070,401, Hirai and Miyata describe a method for the preparation of a halogenated aromatic amine, wherein, a halogenated aromatic nitro compound is hydrogenated in liquid phase in the presence of a platinum-base catalyst to obtain a corresponding halogenated aromatic amine. The hydrogenation is carried out in the presence of an alkylmonoamine, an alicylic amine or a polyalkylenepolyamine The main drawback of the process is that it takes a longer reaction time, i.e. 40 to 210 minutes, depending upon the substrates and a pressure of about 50 kg/cm2, although the conversion was 88.7 to 98.5%.
Reference may be made to U.S. Pat. No. 4,375,550, wherein the hydrogenation of halogen-substituted aromatic nitro compounds to corresponding amino compounds were carried out at elevated temperature (50-200° C.) and pressure (1-70 atm) using catalysts consisted of platinum, palladium, rhodium, iridium, ruthenium and osmium supported on carbon material. The main drawback of the process is that it involves precious metals as well as the drastic process parameters.
In U.S. Pat. No. 4,760,187, Kosak discloses a process of reducing chloro-nitrobenzenes to corresponding chloroanilines catalysed by metallic ruthenium-platinum at a pressure of 200 to 800 psi and temperature 70 to 160° C. The products generated is contaminated with by-products. Further, prolonged reaction time is required for an economical degree of conversion.
Reference may be made to U.S. Pat. No. 5,068,436, wherein, a process of reducing fluorinated or chloro-nitrobenzenes to corresponding haloanilines in presence of noble metals (such as rhodium, palladium, iridium, and platinum) supported on carbon/Raney nickel or cobalt catalyst in acidic catalytic medium is described. The process is associated with pressure (hydrogen) in the range 50 to 2000 psi, temperature 50 to 100° C., time of reaction 1 to 2 h to yield greater than 99%. The isolated yield is 80 to 90%. The main drawback of the process was that it involved precious metals, complicated process parameters, higher reaction time and lower isolated yields.
Reference may be made to U.S. Pat. No. 5,105,011, wherein, a process is described for hydrogenation of halogenonitroaromatic compounds in the presence of a nickel-, cobalt- or iron-based catalyst preferably by Raney nickel and hydrogen in the presence of iodine at a temperature from 50 to 150° C. and preferable pressure 1 to 100 bar. The main drawback of the process is that it involves some cumbersome steps, high pressure and a mixture of products were obtained.
Reference may be made to U.S. Pat. No. 5,126,485, wherein, a process is described for hydrogenation of halogenonitroaromatic compounds in the presence of a nickel-, cobalt- or iron-based catalyst preferably by Raney nickel and hydrogen in the presence of a sulfur-containing compound like sulfoxide or sulfone, at a temperature from 50 to 150° C. and preferable pressure 1 to 100 bar. The main drawback of the process is that it is associated with some cumbersome steps, high pressure and a mixture of products were obtained.
In U.S. Pat. No. 7,288,500 B2, Liu et al., describes a process wherein, hydrogenation of halonitroaromatic compounds is carried out in the presence of supported (carbon black, activated carbon, silica, alumina etc.) metals (palladium, platinum, ruthenium and rhodium) complexes of acetylacetone backbone ligands followed by reduction at temperature less than 160° C. The catalytic reduction is carried out at temperature 0 to 160° C., pressure 1 to 100 bar and reaction time 10.25 to 13.5 h to yield mixtures of compounds (selectivity 76 to 97%). The main drawback of the process is that the process involves several complex steps of catalysts preparation and yields were impure products.
Reference may be made to U.S. Pat. No. 7,381,844, wherein, a process is described for hydrogenation of chlorinatednitrobenzene at temperature 40 to 150° C. and pressure 5 to 40 atm in the presence of nanosized boron-containing nickel catalyst within a reaction time 10 to 80 minutes to give conversion 20 to 100% and selectivity higher than 99%. The main drawback of the process is that the process involves several complex steps of catalysts preparation and higher reaction time to yield higher selectivity. The aforementioned U.S. patents are hereby incorporated by reference herein.
Chinese Patent No. CN101745382, discloses a catalyst for synthesizing parachloroaniline from parachloronitrobenzene by hydrogenation and a preparation method thereof. The active component of the catalyst is Pt, the carrier is attapulgite, and the content of the Pt is in the range of 0.1 wt % to 5 wt %. The catalyst not only has high activity, but also effectively inhibits the generation of a dechlorination reaction. Under the condition that the parachloronitrobenzene is completely transformed, the selectivity of 100% for the parachloroaniline is realized. The attapulgite clay with a mineral acid acidified (sulfuric acid or hydrochloric acid) to a concentration of 2-10 wt %. Polyvinyl pyrrolidone and chloroplatinic acid-treated attapulgite were obtained after the acid solution was stirred at room temperature and dried to obtain a catalyst precursor. Finally, the catalyst precursor in a stream of hydrogen at 200˜500° C. reduction of 2 to 10 h was used to obtain a catalyst by filtration, washing and drying procedure. The invention does not disclose the particle size of the Pt catalyst nor the surface area of the modified attapulgite matrix after acid modification. The overall process of the invention is cumbersome and lengthy. Chinese Patent No. CN101745382 is hereby incorporated by reference herein.
Reference may be made to F. Wang et. al. Chem. Commun, (2008) 2040-2042, wherein, liquid phase hydrogenation of p-chloronitrobenzene in methanol is carried out at 40° C., H2 pressure in the range 20-40 bar and time of reaction from 20 to 275 minutes in presence of polyvinylpyrrolidone protected platinum nanoparticles supported on layered zirconium phosphate in order to obtain conversion 74 to 100% and selectivity 94 to 100%. The main drawback of the above process is that it involves higher pressure and longer reaction time.
Zhang et. al. reports (J. Catalysis, 229, 2005, 114-118) that use of Pt/γ-Fe2O3 catalyst results in about 100% conversion of o-chloronitrobenzene to o-chloroaniline within 10 to 392 min with conversion 49 to 100% and selectivity 45 to 99.9%. The reaction was carried out in methanol at a temperature 60° C. and pressure 10 to 40 bar. The main drawback of the process is that it involves considerably high pressure.
Reference may be made to Chang et. al., J. Colloid & In. Sc. 336 (2009) 675-678, wherein it reports that platinum nanoparticles, immobilized in PEGs, catalyze hydrogenation of o-chloronitrobenzene with conversion 31 to 100%, selectivity 84 to 99.7%, within a reaction time from 30 to 600 min, temperature 40 to 80° C., and pressure 10 to 50 bar. The conversion and selectivity were lowered by the aggregation of Pt particles because the amount of PEG is not enough to protect platinum nanoparticles. Another drawback of the process is that the separation of catalyst from the reaction mixture is not simple.
Xiao et. al. reports (J. Catalysis, 250, 2007, 25-32) that use of platinum nanoparticles stabilized by ionic liquid like copolymer catalyst results in 77.5% to 95.9% conversion of o-chloronitrobenzene to o-choloroaniline and 95.1% to 99.9% selectivity within a period from 0.83 to 1 h. The reaction is carried out at a temperature of 60° C. and 40 bar H2 pressure. The main drawback of the process is that it involves high pressure.
Reference may be made to Corma et. al. (J. Am. Chem. Soc. 130, 2008, 8748-8753), wherein hydrogenation of substituted nitroaromatics are carried by using platinum nanoparticles supported by TiO2 in tetrahydrofuran (THF) with 95% selectivity within a period of 0.35 to 6.5 h. The reaction is carried out at temperature 45° C. and 3 to 6 bar h2 pressure. The main drawback of the process is that it takes high time for the complete conversion.
Reference may be made to Liu et. al. (Synlett, 2009, 595-598) wherein, hydrogenation of o-chloronitrobenzene is carried out by using platinum nanoparticles supported carbon catalyst in ethanol with 100% conversion and 66.5 to 99.4% selectivity. The reaction is carried out at 25° C. and 10 bar H2 pressure within 4.5 to 10 h. The main drawback is that the process is time consuming and selectivity is low.
Reference may be made to Motoyama et. al. (Organic Lett., 11, 2009, 1345-1348), wherein, the hydrogenation of m-chloronitrobenzene and o-chloronitrobenzene is carried out by polysiloxane gel encapsulated platinum nanoparticles in ethyl acetate with conversion in the range 63 to 99%. The reaction is carried out at 25° C., 10 atm H2 pressure and for 24 h. The main drawback of the process is that it requires a long time for the reaction.
Reference may be made to Dutta et al. (Synthesis and catalytic activity of Nio-acid activated montmorillonite nanoparticles, Applied Clay Science 53, 2011, 650-656), wherein, the montmorillonite clay is modified by acid activation with mineral acid under controlled condition for generating nanoporous materials for using as support for Nio-nanoparticles. The supported Nio-nanoparticles showed efficient activity in transfer hydrogenation of acetophenone to 1-phenylethanol with high very efficiency. The aforementioned journal articles are hereby incorporated by reference herein.